In an undisturbed sequence of layers of rocks, the younger layers lie on top of the older layers
The one with higher mass has a higher density because it fits more mass into the same amount of space (volume).
I'm not sure how many sign fig's you are required to have.
However I think the final answer would be 0.05 Moles, because of the .5g, that is considered 1 sign fig.
The correct answer is C 0.15 g/mL.